1. Field of the Invention
This invention relates to multi-beam communications satellites, and more specifically to flexible dynamic allocation of power to high power amplifiers to meet varying traffic conditions while maintaining amplifier efficiency.
2. Description of the Related Art
Many modern satellite systems utilize multiple spot beams to allocate capacity to users located in different geographic regions. Examples of these systems range from Fixed Satellite Services (FSS) where a few large beams are used to distribute higher bandwidth data to Mobile Satellite Services (MSS) where, in the next generation systems, several hundred spot beams will be used to connect digital voice and low rate data between mobile and fixed users and local gateway stations with connections to the Public Switched Telephone Network (PSTN).
To ensure clear reception at the receiving stations, the satellite must amplify the uplink signals to provide a strong downlink signal. However, the available power on an orbiting satellite is limited by the amount of power generated by the satellite's solar panels. Known systems allocate a fixed amount of power to each channel. As a result, when traffic on the channel is light, power is wasted and when traffic is high the amplifiers saturate such that the amplification is insufficient to ensure clear reception.
Crampton, et al, U.S. Pat. No. 5,119,042, which is assigned to Hughes Aircraft Company, the assignee of the current application, discloses a method of dynamically adjusting each channel amplifier's operating point to maintain operation in the linear region without saturating. Crampton, et al, measures the power levels of the received uplink signal and the amplified output signal and adjusts the amplifier's operating point so that it operates in its linear region. The system does not monitor the power requirements of other channels. Nor does it allocate unused power from one channel to a channel with heavier signal traffic.
Another known power allocation system uses fixed solid state power amplifiers in a Butler Matrix configuration. The Butler Matrix configuration described in Sandrin, "The Butler Matrix Transponder", COMSAT Technical Review, Vol. 4, No. 2, Fall 1974, pages 320-321, uses two complementary Butler Martix networks. One precedes and the other follows a set of amplifiers. The networks distribute and collect each signal to and from each amplifier. This configuration offers a flexible power sharing by distributing the incoming signals among the amplifiers and redistributing the amplified signals to their respective outputs. Using the Butler Matrix configuration, optimum performance is achieved when the signal power of all channels is equal. This system does not, and is not intended to, allocate spare power to channels experiencing heavier traffic. Rather, Sandrin amplifies all input signals equally.